Missions Astéroides

Concepts For Asteroid Missions Proposed

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President Barack Obama’s call for a mission to send astronauts to an asteroid has scientists and engineers pondering just what it would take.
While Congress and the White House have yet to settle on an exploration policy to replace the Bush administration’s lunar-return goal, the Augustine panel’s call for a “flexible path” into the Solar System beyond low Earth orbit, and Obama’s endorsement of a human mission to an asteroid has opened up planning across the aerospace community.
Just as NASA’s Constellation program was working on robotic precursor missions before a lunar landing that originally was set for about 2020, a mission that would reach an asteroid by about 2025, as the president suggested, probably also would require robotic scouting visits. And for a human mission there already is a concept that would use the Orion crew exploration vehicle under development for Constellation as the basis for a longer trip to an asteroid.
Lockheed Martin says its Plymouth Rock mission proposal would reach a near-Earth asteroid with astronauts using two Orion capsules and a dual-launch strategy as early as 2016—nearly a decade ahead of the asteroid goal Obama outlined in April (AW&ST April 19, p. 28).
Six-month missions, as soon as 2016 or 2019, with two astronauts would reach out to a class of recently discovered asteroids, most no more than 30-240 ft. in diameter, in nearby orbits that pose difficulties similar to a lunar landing.
Samples gathered by astronauts at these rocky bodies left in the formation of the planets would reveal more about the Solar System’s evolution, offer insight into the composition of objects posing a potential collision threat to Earth and prepare explorers for a Mars mission.
“We concluded it was not as difficult as we expected,” says Josh Hopkins, principal investigator at Lockheed Martin for advanced human exploration missions, of a three-year company study on expanding Orion’s lunar mission role. “The design requirements for a lunar mission are close enough to an asteroid mission that we were able to extend the design.”
Orion’s solar power, robust propulsion and 210-day flight duration underpinned the new mission. Though Orion’s radiation protection is another key asset, Hopkins says it requires further study.
Congress has yet to fully address the White House proposal to terminate NASA’s Constellation back-to-the-Moon program in favor of an initiative to develop commercial orbital space transportation systems and aim for the human exploration of an asteroid in 2025.
The House favors preserving much of Constellation’s systems, including the Orion capsule and Ares launchers for flights to the International Space Station and deep-space destinations. The Senate version calls for a crew capsule and heavy-lift launcher that would be ready for deep-space missions by the end of 2016. Both converge on Mars as an ultimate destination.
Plymouth Rock includes the launch of a crewed Orion on a Delta IV or Ares I launcher, following the launch of an unmanned heavy-lift rocket slightly smaller than the proposed Ares V. The first launch would place a supplemental Orion and an Earth departure stage in orbit. Once linked, the Orion capsules—docked nose-to-nose—and the departure stage would start an outbound journey of about three months.
The proposed destination for a 2016 launch is asteroid 2008 HU4, 20-35 ft. in diameter, at an encounter distance of 2.5 million mi. In 2019, asteroid 2008 EA 9, of the same dimensions and 7.5 million mi. distant, could be accessible.
Other studies have found at least 44 near-Earth objects that could be reached by 2025, but missions to those much larger space rocks would require the equivalent of the proposed Ares V heavy-lift rocket (AW&ST Aug. 16, p. 30).
In the Lockheed Martin concept, astronauts would rendezvous with their small targets but not attempt to land. Using spacewalking techniques pioneered outside the space shuttle and ISS, relying on tethers or possibly the free-flying Manned Maneuvering Unit, they would float over to the asteroid for five days of sample collection and analysis.
That approach is fine, as far as it goes, says Andrew Cheng, chief scientist in the space department of the Johns Hopkins University Applied Physics Laboratory in Columbia, Md. But sending a robotic mission to learn more about the surface properties of asteroids before committing humans to a trip would likely enable the astronauts to do a lot more useful work once they get there.
“If you’re going to mount a human mission to an asteroid, are you just going to have them look out the window, or maybe barely touch it?” Cheng says.
Cheng has been part of both robotic missions to reach an asteroid, as lead scientist on NASA’s Near Earth Rendezvous Mission (NEAR) and a member of the science team on Japan’s Hayabusa sample return mission. Drawing on that experience, he and his colleagues are studying a “Next-Gen NEAR” that would use commercially available components wherever possible and lightweight cameras, spectrometers and other surface-analysis gear to hold the probe’s weight to something that could be launched on a medium-class rocket, perhaps with a secondary payload as well.
Cheng says a robotic probe could be launched as early as 2014 and urges planners to concentrate on the largest bodies that can be reached.
“They need to be very nearby and accessible,” he says. “They ought to be not too tiny. I don’t think it’s good to send astronauts to a target that’s smaller than the space station, which many of the targets under discussion are. . . . The bigger targets are more interesting, you have a better chance of finding varied geology, composition, that sort of thing.”